As known, commercial vehicles have elements for supporting the wheel-rims or hubs, robust enough to bear heavy transport loads.
Typically, these hubs are connected to axles by means of bearings, which allow free rotation of the hub and thus of the wheel-rim connected thereto. In cases where these hubs are used for commercial vehicles, the bearings, accommodated in the hub, are required to bear even extremely heavy loads. Though the friction between the axle and the hub is particularly low, due for example to the use of roller bearings, should the action to be transmitted through the bearing be particularly high there occurs a considerable heating of the bearing and of all components adjacent thereto. This heating should be suitably discharged so as not to jeopardise the correct operation of the bearings accommodated in the hub and thus possibly of the disc brake disc connected thereto.
Upon actuation, also the braking system causes a specific production of heat. The braking action of the vehicle transforms, due to the friction between the components thereof, kinetic energy into thermal energy. The fact that the disc brake disc is connected to the support hub of the wheel-rim, causes, in case of frequent and intense braking actions, for example in cases in which the vehicle is travelling descending an alpine pass, a high raising of the temperature of the disc brake disc and also of the portions thereof connected to the hub also causing a considerable heating of the hub and of the bearing accommodated therein. At times, failure to suitably cool the brake may jeopardize not only the correct operation of the disc but also of the bearing.
Therefore, there arises a particular need of finding and providing a solution capable of allowing suitably cooling not only the disc brake disc, but particularly the interface between the disc brake disc and the hub which accommodates the bearing.
Solutions having means for the passage of cooling air to the base of the disc brake disc, particularly to the base of the braking band thereof, are known.
For example, document IT 1 147 976 has a disc brake disc connected to a hub provided with a flange which moves the disc away from the cylindrical portion of the hub suitable to accommodate the bearing. In addition, this known solution has, in the cylindrical drum-shaped portion for connecting to the hub, openings arranged slightly after the braking band, suitable to circulate cooling air around the braking band, the air then being conveyed to specific sheets fixed onto the rim outside the wheel.
Though satisfactory from various points of view, this prior art embodiment requires a considerable radial overall dimension to move the disc brake disc away from the portion of the hub suitable to accommodate the bearing. Furthermore, this prior art solution allows the circulation of cooling air solely in proximity to the portion of the hub facing the vehicle, leading to non-uniform cooling of the hub and of the bearing contained therein.
Also document DE 39 42 651 shows a solution similar to the aforedescribed one for use in a vehicle, wherein the disc brake disc is of the ventilated type.
Though satisfactory from various points of view, this solution is particularly more indicated for cooling the braking band than the hub and the bearing contained therein. As a matter of fact, in order to convey the air around the braking band better, provided for is a sheet arranged inside the disc brake disc which separates the braking band from the hub, pushing the air towards the openings provided for in the connection portion between the braking band and the drum so as to obtain maximum cooling possible in proximity to the braking band. Should the heat generated by the braking action not be suitably released and thus traverse the drum reaching the hub, for example due to the low speeds of the vehicle, this prior art solution would not allow further and separate cooling aimed at avoiding malfunctioning of the bearing.
Document FR 1 491 828 shows a braking system solution also in which a disc brake provided with a drum having openings not specifically developed for the aeration of the hub is shown.